This invention relates generally to a combustor liner, and more particularly to a combustor liner that includes cooling holes.
Typically, a combustor for a gas turbine engine includes an outer casing and an inner liner. The liner and the casing are radially spaced apart to form a passage for compressed air. The liner forms a combustion chamber within which compressed air mixes with fuel and is ignited. The liner includes a hot side exposed to hot combustion gases and a cold side facing the passage formed between the liner and the casing. Liners can be single-wall or double-wall construction, single-piece construction or segmented construction in the form of discrete heat shields, panels or tiles.
Typically, a plurality of cooling holes supply a thin layer of cooling air that insulates the hot side of the liner from extreme combustion temperatures. The liner also includes other openings much larger than the cooling holes that provide for the introduction of compressed air to feed the combustion process. The thin layer of cooling air can be disrupted by flow through the larger openings potentially resulting in elevated liner temperatures adjacent the larger openings. Elevated or uneven temperature distributions within the liner can promote undesired oxidation of the liner material, coating-failure or thermally induced stresses that degrade the effectiveness, integrity and life of the liner.
It is known to arrange cooling holes in a dense grouping upstream of larger openings to distribute ample cooling airflow in regions via film cooling and effective heat removal through the thickness of the liner by convection along the surfaces of the holes. Disadvantageously, the greater flow through the larger openings can disrupt the flow of cooling air around the larger opening. This situation can result in a deficiency of cooling air downstream of the larger opening causing an undesirable increase in liner temperature. Further, the amount of cooling airflow is limited for design intent and it is therefore desirable to efficiently allocate available cooling airflow to provide even temperature distribution throughout the liner.
Accordingly, it is desirable to develop a combustor liner that improves cooling layer properties adjacent to large openings to eliminate uneven temperature distributions or undesirable temperature levels.